This application relates to mobile telecommunications systems in general, and in particular relates to a method and apparatus for searching for and reporting Public Land Mobile Networks “PLMNs” in a mobile telecommunications system
In a typical cellular radio system, mobile user equipment (UE) communicates via one or more radio access radio networks (RANs) to one or more core networks. User equipment (UE) or mobile devices comprises various types of equipment such as mobile telephones (also known as cellular or cell phones), lap tops with wireless communication capability, personal digital assistants (PDAs) etc. These may be portable, hand held, pocket sized, installed in a vehicle etc and communicate voice and/or data signals with the radio access network.
In the following, reference will be made to UMTS, LTE and to particular standards. However it should be understood that the invention is not intended to be limited to any particular mobile telecommunications system.
A radio access network covers a geographical area typically divided into a plurality of cell areas. Each cell area is served by at least one base station, which in UMTS may be referred to as a Node B. Each cell is typically identified by a unique identifier which is broadcast in the cell. The base stations communicate on radio frequencies over an air interface with the UEs within range of the base station. Several base stations may be connected to a radio network controller (RNC) which controls various activities of the base stations. The radio network controllers are typically connected to a core network.
In wireless telecommunications systems, mobile devices, such as handheld telephone devices, communicate wirelessly with networks known as PLMNs (Public Land Mobile Networks). PLMNs may use one or more radio access technologies. Examples of such radio access technologies are GSM, UMTS, also referred to as UTRA, LTE, also referred to as E-UTRA, CDMA2000 etc.
Typically the mobile devices (which are also known as UEs or User Equipment) communicate with components of the PLMNs, periodically reporting the availability of base stations or network nodes (e.g. Node Bs) for various PLMNs to enable handover between base stations or network nodes as a UE roams geographically or as network traffic on PLMNs varies.
The mobile devices may perform a scan to report the availability of PLMNs. Such a scan may be initiated in various situations, for example at power on, at return from loss of coverage, user initiated and periodically. This information about the available PLMNs may be used internally by the mobile device, for example to automatically select a different PLMN, and may also be reported via a user interface to allow the user to manually select a different PLMN.
In many Radio Access Technologies, a PLMN is uniquely identified by a PLMN identity which may comprise a mobile country code (MCC) and a mobile Network Code (MNC). MCC comprises three digits, of which the first one indicates a world zone (e.g. 3xx indicates North America) and the second and third digits represent individual nations in these zones (for instance the MCC of Canada is 302). The MNC identifies a PLMN in a country. It comprises two or three digits and is allocated by national organisations for mobile telecommunications standards. The PLMN identity uniquely identifies a PLMN.
3GPP Technical Specification number 25.304 v.9.0.0 section 5 (UMTS) (herein incorporated by reference in its entirety) specifies that the UE Access Stratum shall search for and report ‘available PLMNs’ to the UE Non-Access Stratum (NAS). In section 3.1, the term “available PLMN” is defined to mean “A PLMN for which the UE has found at least one cell and read its PLMN identity”. The standard does not specify any requirements beyond reading the PLMN identity. 3GPP Technical Specification number 36.304 v. 9.1.0 (LTE) (herein incorporated by reference in its entirety) is similar.
There are thus proposed strategies for searching for and reporting Public Land Mobile Networks “PLMNs” in a mobile telecommunications system. A number of such strategies are detailed below.
Other aspects and features of the proposed strategy will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of an apparatus and method for searching for and reporting Public Land Mobile Networks “PLMNs” in a mobile telecommunications system.
The same reference numerals are used in different figures to denote similar elements.